1. Field of the Invention
This invention relates to printing presses, and more particularly to a web-fed, multicolor printing press having a plurality of printing units for printing different color images on a continuous web of paper or like printable material. Still more particularly, the invention deals with such a press wherein each plate cylinder is split into three parts, each with a lateral dimension equal to two newspaper pages, for independently carrying as many printing plates thereby concurrently to print images in transverse juxtaposition on the web. Even more particularly, the invention concerns improvements in or relating to means in such a multicolor printing press for fine, independent readjustment of both lateral and circumferential positions of the three parts of each plate cylinder with a view to exact registration of different color images on the web.
2. Description of the Prior Art
It has been known and practiced extensively to split a plate cylinder into two or more parts that are capable of both lateral and circumferential displacement relative to each other. An example is the multicolor newspaper printing press in which each plate cylinder is split into a pair of halves each having two-newspaper-page width. Japanese Patent Publication No. 59-31467 and Japanese Utility Model Publication Nos. 6-11769 and 6-38681 are hereby cited as teaching such split plate cylinders.
Japanese Patent Publication No. 59-31467 and Japanese Utility Model Publication No. 6-11769 both suggest a plate cylinder comprised of a first cylinder part having a reduced diameter core extending coaxially therefrom, and a second cylinder part of tubular shape slidably fitted over the core and having an outside diameter equal to the diameter of the first cylinder part. Adjustments are provided for independently varying the lateral and circumferential positions of the two plate cylinder parts. According to Japanese Patent Publication No. 59-31467, the lateral and circumferential adjustments for the two cylinder parts are both disposed outside the pair of confronting framing walls between which the split plate cylinder is supported. Japanese Utility Model Publication No. 6-11769 differs in providing the lateral and circumferential adjustments for one plate cylinder part on the outside of one framing wall, and those for the other plate cylinder part on the inside of the same framing wall.
Japanese Utility Model Publication No. 6-38681 teaches a plate cylinder comprised of a pair of halves of tubular shape, both slidably mounted on a core of cylindrical shape. The lateral and circumferential adjustments for one plate cylinder half are provided on the outside of one framing wall, and those for the other plate cylinder half on the outside of the other framing wall. Driving torque is first transmitted to the core and thence to the pair of tubular halves, in order that the three constituent parts may be jointly rotatable, and that the pair of tubular halves may be independently adjustable circumferentially.
The three foregoing citations are alike in teaching two-part plate cylinders but silent on the division of a plate cylinder into three. Japanese Utility Model Publication No. 6-11769 in particular has an additional problem arising from the placement of all the lateral and circumferential adjustments for the two plate cylinder parts in the neighborhood of one of the pair of framing walls. As one lateral, and one circumferential, adjustment are positioned on the inside of that one framing wall, the distance between the two framing walls must of necessity be much longer than in the absence of such adjustments. The long span between the walls has made it necessary to provide a plate cylinder having a pair of correspondingly elongate trunnions, which of course are much slender than the plate cylinder itself. The plate cylinder has therefore been easy to sag under its own weight, with consequent difficulties in lateral and circumferential displacement of the two plate cylinder parts due to a rise in frictional resistance.
It has also been known to split a plate cylinder into four parts, each one newspaper page wide, as disclosed for example in Japanese Patent No. 2,726,716. The four-part plate cylinder comprises a solid cylinder part which has one or two newspaper pages width and which has rod-like cores of smaller diameter extending coaxially therefrom, and hollow cylinder parts which are each one or two newspaper pages wide and which are slidably mounted to the cores. Lateral and circumferential adjustments are provided for each of the solid and hollow plate cylinder parts. The adjustments for the solid plate cylinder part lie on the outside of one of the pair of framing walls, and those for each hollow plate cylinder part on the outside of that one of the pair of framing walls which is closer to that hollow plate cylinder part. Where two lateral, and two circumferential, adjustments are provided, the lateral adjustment for the plate cylinder part located centrally of the plate cylinder is mounted to the bearing sleeve supporting the plate cylinder, and the circumferential adjustment for that plate cylinder part is mounted to the blanket cylinder adjoining the plate cylinder in question.
An objection to this prior art four-part plate cylinder is the extreme complexity of the lateral and circumferential adjustments. Another serious disadvantage is that the lateral displacement of the solid plate cylinder part causes simultaneous displacement of a helical gear constituting a part of the drive linkage to that plate cylinder part, resulting in simultaneous angular displacement of the plate cylinder part by reason of the twisted gear teeth. Lateral displacement has thus been not independent of circumferential displacement.
Attempts have been made in recent years to make plate cylinders greater in diameter or length with a view to higher production, aside from an increase in printing speed. Japanese Unexamined Patent Publication No. 9-141826 represents an example of such conventional attempts at longer plate cylinders. It is not disclosed, however, to divide such a long plate cylinder into several parts that are independently displaceable both laterally and circumferentially.
The present invention has it as an object to provide a three-part plate cylinder for use in a web-fed, multicolor offset printing press or the like, so made that the three plate cylinder parts are independently adjustable both laterally and circumferentially for registration.
Another object of the invention is to make the three-part plate cylinder itself and the lateral and circumferential adjustments therefor as simple, compact and inexpensive as feasible in construction.
Still another object of the invention is to arrange the lateral and circumferential arrangements in such a manner that the span between the pair of confronting framing walls is kept at a minimum in order to prevent the three-part plate cylinder from sagging under its own weight.
Briefly, the present invention concerns, in a web-fed printing press having a series of printing units for printing images on a continuous web of paper or like material, a three-part plate cylinder apparatus included in each printing unit. The three-part plate cylinder apparatus comprises a plate cylinder which is rotatably supported between a pair of spaced-apart framing walls or like means and which is split into three. The three parts of the plate cylinder are capable of displacement both laterally and circumferentially independently of one another for registration. Drive means are coupled to the three parts of the plate cylinder for jointly driving them during printing. Also included are lateral adjustment means which are mounted outside the framing means and which are coupled to the three parts of the plate cylinder for causing lateral displacement of each part independently of the other parts, and circumferential adjustment means which are mounted outside the framing means and which are coupled to the three parts of the plate cylinder for causing circumferential displacement of each part independently of the other parts.
The three parts of the plate cylinder consist of a center part having a first and a second trunnion coaxially extending in opposite directions therefrom through the pair of framing means, a first end part having a first hollow shaft slidably fitted over the first trunnion of the plate cylinder center part, and a second end part having a second hollow shaft slidably fitted over the second trunnion of the plate cylinder center part. The three parts of the plate cylinder are jointly drivable as by gears coupled to either of the trunnions of the center part and to the hollow shafts of the two end parts. The lateral and the circumferential adjustment means for the three parts of the plate cylinder are also coupled to the trunnions of the center part and to the hollow shafts of the two end parts, all on the outsides of the framing walls. The lateral and circumferential adjustment means for the center part of the three parts of the plate cylinder are mounted outside in separate frame means, respectively.
When the images printed by the different printing units of the press are found to be out of register, any of the center part and two end parts may be repositioned in either or both of the lateral and circumferential directions as required for registration. Such positional readjustment is possible during the progress of printing. Each plate cylinder part is readjustable totally independently of the others, and the displacement of each plate cylinder part in either of the lateral and circumferential directions does not affect its position in the other direction.
Since the lateral and the circumferential adjustments for the three parts of the plate cylinder are all mounted outside the framing walls as above, these walls can be spaced from each other a distance just needed to accommodate the plate cylinder itself therebetween. The sagging of the plate cylinder under its own weight can thus be reduced to a minimum, assuring stable rotation for printing and smooth lateral and circumferential displacement of the plate cylinder parts for registration.
In the preferred embodiments of the invention to be disclosed subsequently, each plate cylinder part is capable of carrying a printing plate that has two newspaper pages width. The plate cylinder as a whole is capable of concurrently printing six newspaper pages. For production of 48-page newspapers, therefore, the invention requires only four double-side printing units, compared to six such units heretofore required by machines employing four-newspaper-page plate cylinders. The reduction of the printing units is tantamount to that of the distance the web of paper is required to travel from the infeed to the folding station, and, in consequence, to that of the amount of paper wasted while being threaded along the predefined path through the press. Additionally, the invention also results in a decrease (to two thirds) of the pastings required from one web to another, and of the waste of paper resulting from pasting failures.
The above and other objects, features and advantages of this invention and the manner of realizing them will become more apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference had to the attached drawings showing the preferred embodiments of the invention.